A bacteriophage life cycle offers a model system for study of the control of a programmed sequence of events in a biological system. With the objective of gaining increased understanding of biological regulatory mechanisms, we propose to study several of the mechanisms controlling the sequence of early events in infection of Bacillus subtilis by bacteriophage SPO1. Using sequential complementation experiments, we will determine to what extent the observed heterogeneity in time of function of various early genes is necessary for successful phage infection, and we will determine the relationship between the sequence in function of the early genes and the sequence in activity of their gene products. The culmination of the sequence of early events is the initiation of DNA replication. By superinfection experiments, identification of initiation-deficient mutants, and analysis of these mutants in sequential complementation, we will attempt to characterize the mechanisms by which the timing of initiation is regulated. BIBLIOGRAPHIC REFERENCES: Glassberg, J.S., Slomiany, R., and Stewart, C. "A Screen for Replication-Deficient Mutants", Abstracts of Cold Spring Harbor Bacteriophage Meeting, p. 45, 1975. Cregg, J.M. and Stewart, C. "Timing of Initiation of DNA replication in SPO1 Infection of Bacillus subtilis." Abstracts of Cold Spring Harbor Bacteriophage Meeting, p. 46, 1975.